Pressure sensors may be used in various environments. A pressure sensor may detect the pressure in oil wells, automobile environments, and others, for example. This detection of pressure is conventionally used to determine the amount of oil remaining in the oil well. An oil well, however, may be a relatively harsh environment. Use in an oil well may require operation at high-pressure, for example 10,000 psi, and at high operating temperatures, e.g. 150 degrees C.
Surface micromachined pressure sensors are known. However, the design and process of many of these sensors have been optimized for low pressure applications.
Certain high-pressure sensors have been reported using silicon xe2x80x9cbulkxe2x80x9d micromachining. This technology has a number of disadvantages. A serious problem is the difficulty of overpressure protection so that the diaphragm may crack if an over range pressure is applied. Also, the thickness and dimension of the diaphragm, which are essential for the performance of the pressure sensor, is difficult to control precisely by bulk micromachining. Bulk micromachined sensors also often require wafer bonding, which sometimes introduces a thermal mismatch problem.
In contrast, a surface micromachined high-pressure sensor has inherent overpressure protection and more precise dimension control. In addition, the device may also be able to be formed in a smaller size and there is no need for wafer bonding and double-side alignment. Moreover, the process may be no more complicated than other similar systems.
The present system describes a surface micromachined pressure sensor that may be operable in high-pressure, high temperature applications. The sensor as disclosed herein preferably has structure capable of operation at pressures higher than 6000 psi, and in fact, the present system may be usable at a pressure range of 10,000 psi, 14000 psi, or even 30000 psi or higher.
In an embodiment, the device may be a device with a silicon nitride diaphragm, using the piezoresistive operating principle. Special techniques are disclosed to enable small size, inherent overpressure protection, precise dimension control, ease of packaging, and others.